1. Field of the Invention
The present invention relates to a stamper used to form a concave/convex pattern by imprinting, a method of forming a concave/convex pattern on a substrate using such stamper, and a method of manufacturing an information recording medium using a concave/convex pattern formed according to such method.
2. Description of the Related Art
As one example of a method of forming a concave/convex pattern using this type of stamper, the specification of U.S. Pat. No. 5,772,905 discloses a nano-imprint lithography method (i.e., a method of forming a concave/convex pattern of nanometer size: hereinafter simply “imprinting method”) that forms a concave/convex pattern of nanometer size on a substrate by pressing a stamper (“mold”) on which a concave/convex pattern of nanometer size has been formed onto a resin layer on a substrate to transfer the concave/convex pattern of the stamper to the resin layer. In this method of forming a concave/convex pattern, polymethyl methacrylate (PMMA: a resin material) is first spin coated on the surface of a substrate made of silicon to form a resin layer (“thin film layer”). Next, after both a multilayer structure, which is composed of the substrate and the resin layer, and the stamper have been heated, as shown in FIG. 1B of the U.S. patent, the entire area of the stamper is pressed onto the resin layer on the substrate with a predetermined pressure. Next, the multilayer structure is left in this state with the stamper pressed thereupon until it reaches room temperature (i.e., a cooling process is carried out), and after this the stamper is separated from the resin layer. By doing so, as shown in FIG. 1C of the U.S. patent, the concave/convex pattern of the stamper is transferred to the resin layer so that concave parts (regions) are formed at the positions where the convex parts were pressed in and convex parts are formed at the positions of the concave parts of the stamper, thereby forming a concave/convex pattern of nanometer size on the substrate (i.e., in the resin layer).
On the other hand, Japanese Laid-Open Patent Publication No. 2003-157520 discloses a method of forming a concave/convex pattern where the occurrence of transfer defects in the concave/convex pattern due to reasons such as tilting of the stamper (matrix) with respect to a base plate to be transferred is avoided by carrying out imprinting in a state where an elastic body (buffer layer) is provided between a stamper and a press and/or between the base plate to be transferred and the press. More specifically, in this method of forming a concave/convex pattern, the base plate to be transferred is set in the press with the surface on which a resin layer (a resist film) is formed facing upward and the stamper is set in the press with the concave/convex pattern formation surface on which the concave/convex pattern to be transferred is formed facing downward. When doing so, an elastic body formed of a soft material such as a PET sheet is sandwiched between the stamper and the press (the press surface), for example. Next, by lowering the stamper toward the base plate to be transferred, the concave/convex pattern of the stamper is pressed onto the resin layer on the base plate to be transferred. When doing so, the elastic body sandwiched between the stamper and the press (the press surface) deforms and therefore tilting of the stamper with respect to the base plate to be transferred and partial warping of the stamper are corrected so that the entire stamper can be pressed onto the resin layer on the base plate to be transferred in a substantially parallel state. By doing so, the concave/convex pattern of the stamper is transferred to the resin layer, thereby forming a concave/convex pattern on the base plate to be transferred.